Research objectives are to evaluate the relationships that exist between the visual pigments and visual apparatus of aquatic vertebrates, those aspects of their behavior that require vision, and the photic- environment. In specific terms the studies will attempt to relate the types of retinal cells and rod and cone pigments found in a given fish with intensity and hue of light against which the fish must detect objects. Fishes with different ecological requirements, feeding behavior for example, will be compared by determining the types of visual pigments and visual cells in different areas of the retina. These findings will be related to the actual photic conditions that exist in the various fields of regard where the fish lives. Emphasis will be placed on fishes characteristic of estuaries and lakes of North America. In addition, attempts will be made to correlate what are believed to be extractable cone pigments with specific cone receptors. A more complete comparative picture than now available of how the eye is adapted to accomplish a visual task should result.